During the past few years the fields of health studies, semiconductor manufacture and environmental protection have presented increasingly stringent demands on the designers of analysis instruments for higher sensitivities during trace analyses. An urgent example is the current need to analyze the stratosphere for fluorocarbons and their derivatives. The reason for the urgency is that Freon 11 and Freon 12, which have been developed and valued largely because of their useful chemical properties, apparently are not destroyed in the lower atmosphere by chemical reactions but slowly diffuse upwards into the upper atmosphere. Upon reaching the stratosphere it is believed that these compounds are decomposed by ultraviolet radiation from the sun, with the resulting release of free chlorine atoms. It is thought that these free chlorine atoms then may act to decrease gradually the average concentration of ozone by means of catalytic chain reactions.
The principal reason why fluorocarbon releases to the atmosphere are considered to be of such potential importance is that a reduction in average long-term concentration of ozone would result in an increase in the amount of ultraviolet radiations reaching the earth's surface. This increase in ultraviolet radiation is postulated to increase skin cancer and it is feared that the growth and development of certain plant and animal species might also be altered.
The problem with fluorocarbons is of sufficient concern that unless new scientific evidence is found to remove the cause for concern it would seem necessary to restrict use of Freon 11 and Freon 12 to the replacement of fluids in existing refrigeration systems. All other uses for these fluorocarbons would be banned. The impact of such restrictions, which have been proposed to start in 1978, can be estimated from the fact that there were at least 2 billion pounds of these fluorocarbons produced in 1973 and it is estimated that a million workers would be affected by restrictions upon fluorocarbon use.
It is clear that direct measurement of chlorine and chlorine oxide are urgently needed. However, the problems are severe because calculations indicate that stratospheric chlorine will be found in concentrations of 3 .times. 10.sup.-.sup.13 to 3 .times. 10.sup.-.sup.12 concentration by volume (10.sup.5 to 10.sup.6 molecules per ambient cm.sup.3) and chlorine oxide in concentrations of 3 .times. 10.sup.-.sup.11 (10.sup.7 molecules per ambient cm.sup.3) at 30 kilometers height. The present invention describes an apparatus that could be used for Cl and F measurements in the concentrations described. It would be valuable in measuring small concentrations of any electronegative atom, molecule or radical.
Devices are presently commercially available for the efficient conversion of electronegative particles into a well controlled high velocity stream of negative ions. One such device is manufactured by General Ionex of Ipswich, Mass. By directing the emerging particles in a stream such that each passes successively through a small mass analyzer, a charge exchange dissociater, an appropriate arrangement of electric and magnetic fields and finally into an energy sensitive detector, it is possible to over-determine the kinetic parameters of each particle and provide a real time unique identification. Because these procedures virtually eliminate molecular contributions and other scatter backgrounds, sensitivities for Cl greater than 1/10.sup.14 by volume can be achieved.
Also there are many similarities between the principles of the present invention and those underlying the design of nuclear research accelerators of the tandem type. High voltage particle accelerators using charge transfer processes are described in U.S. Pat. No. 3,353,107 and elsewhere. Because of these similarities there exists a wealth of directly applicable design experience and theoretical information which can be applied to the present invention.